Synthetic aperture radar (SAR) is a well known technique for developing radar imagery with excellent two-dimensional (2D) resolution. This is typically done by flying an airplane over the ground to be mapped, and successively transmitting a sequence of radar pulses. With the forward motion of the airplane, each successive radar pulse is transmitted from a position a little farther along on the flight path, thus simulating a very long radar array.
Return signals from the transmitted pulses are sampled in the airplane and either processed on board for immediate exploitation or stored or transmitted for processing at another site. The processing is computationally expensive, employing such techniques as fast Fourier transform (FFT), inverse FFT or correlation on vast amounts of data. These operations require vast processing power and storage.
Radar energy is transmitted in the form of sequential pulses, at different time instances in the flight path of the vehicle. The pulses interact with the terrain (and any object on the terrain) and a portion of the pulse energy is reflected back towards the platform and recorded by a detector. Returns from different objects arrive at different times at the detector. These time differences provide information on range, which is then used to create a final radar image.
Typically, the transmitted pulses in a SAR system are sinusoidal in nature. The detector records the reflected sinusoids by recording a complex number, whose phase component is directly related to the time-of-flight, or range, and its magnitude component is proportional to the reflected energy. Thus, data captured in a SAR system is complex in nature, with properties that are unique with respect to data captured in systems from other imaging modalities.
Technology trends in the field of SAR indicate that SAR system designs are continuously pushing the envelope for increases in area coverage and resolution. These trends imply massive amounts of collected data, which in turn, stress the ability to store collected SAR data and rapidly disseminate SAR data.
Progress in microelectronics and computer technology, together with the creation of networks operating at various channel capacities, has been the basis of an infrastructure for a new era in telecommunications. Standards for the efficient representation and interchange of digital images (like JPEG, JPEG2000) have been essential in the development of digital photography applications. Unfortunately, largely due to the uniqueness of SAR data, data compression algorithms employed by current standards (like JPEG, JPEG2000) do not perform optimally with SAR data.
The present invention addresses this problem by providing a system and method for lossy compression of complex SAR data.